1. Field of the Invention
The invention relates to a control circuit, specifically relates to a causal function circuit for a synchronous rectification in a secondary-side controlled power converter to prevent the power converter from gate overlapping.
2. Description of Related Art
An offline power converter includes a power transformer to provide isolation from an AC line voltage to the output of the power converter for safety. In recent development, applying a synchronous rectifier in the secondary side of the power transformer is to achieve a high efficiency conversion for power converters.
In a conventional power converter, a synchronous rectifier control circuit is usually provided to control turning on and turning off of a synchronous rectifier in the power converter.
However, in the conventional technology of the above mentioned power converter, the dead time of causal function will be very sensitive to the system operation frequency in the power converter. For example, a dead time of causal function is designed according to a low operation frequency (ex. 65 kHz) may not be suitable for the system which operates at a higher frequency (ex. 130 kHz), because the dead time period of causal function may be too narrow to prevent gate overlapping. On the other hand, a dead time of causal function is designed according to a high operation frequency may not be suitable for the system which operates at a lower frequency, because the dead time period will be too wide and result in low efficiency of the system.